Applied online and received a call 5 days later for an interview. I showed up at least 15 minutes early for the interview and was offered a free drink. The manager I interviewed with was very nice, he walked me through the questions and, afterword, went over my availability, what the benefits were, and the dress code. After we finished, he set me up for a second interview at the same location but with a different manager. I arrived at the second interview, again at least 15 minutes early and was offered another free drink. I was interviewed by both the new manager and the manager who had interviewed me the first time. When we'd finished, both managers thanked me and said they would be in touch. A couple of hours after returning home, I received a phone call from the manager who had initially called me, asking for my full date of birth for the background check. Four days later, I received another call with a job offer and I accepted.
My advice is this-- 1) Do dress to impress! It doesn't have to be a full blown suit, but definitely NO jeans.
2) Do some research about the company beforehand. One of the questions I was asked was the good old "Why Starbucks?" and you need to be able to tell them why.
3) Accept the drink! While most may not consider accepting the drink as a test, it does show that you are familiar with AT LEAST one of their products and your interviewer may field you questions such as "What is your favorite drink?" or "Sell me your favorite drink".
4) Starbucks LOVES to ask S.T.A.R (Situation, Task, Action, Result) based questions. While most of the questions are customer service based, you will definitely need to come prepared with specific examples to answer them. Having a previous job will help, but the questions are still answerable even if you're interviewing for your first job.
5) Relax and go in with an open mind! Starbucks, in my experience, is a pretty laid back atmosphere and they're looking for like-minded people. As long as you stay calm, look sharp, and go prepared, you'll be fine.